0:00:07 > 0:00:09February 4th, 1850.
0:00:09 > 0:00:11Work was just starting
0:00:11 > 0:00:14at the Hague Street Printing Press in New York City.
0:00:15 > 0:00:20But, in the basement, temperatures inside their coal-fired boiler
0:00:20 > 0:00:22were reaching dangerous levels.
0:00:23 > 0:00:26A force of nature was struggling to break free.
0:00:34 > 0:00:39At 7.45, a huge explosion tore the building apart.
0:00:41 > 0:00:44Dozens were killed and many more injured.
0:00:46 > 0:00:49The boiler had overheated and exploded.
0:00:55 > 0:00:58Disasters like this were happening daily
0:00:58 > 0:01:00during the Industrial Revolution.
0:01:00 > 0:01:03We'd begun to harness energy,
0:01:03 > 0:01:06but we were struggling to control it with any precision.
0:01:08 > 0:01:10It's perhaps not surprising.
0:01:11 > 0:01:13After all, what is energy?
0:01:13 > 0:01:17Such an intangible thing to measure and understand.
0:01:18 > 0:01:21In this series, I've been exploring how we use measurement
0:01:21 > 0:01:25to quantify every aspect of our world,
0:01:25 > 0:01:29creating a system of seven fundamental units which
0:01:29 > 0:01:33have become the building blocks of modern science.
0:01:33 > 0:01:36From time and distance, to temperature and mass.
0:01:36 > 0:01:40I want to understand how we've imposed order on the universe
0:01:40 > 0:01:43with these basic units of measurement
0:01:43 > 0:01:47and how, through history, each step forward in precision
0:01:47 > 0:01:50has unleashed a technological revolution.
0:01:50 > 0:01:53This programme is all about energy,
0:01:53 > 0:01:58a difficult and dangerous force that comes in many forms.
0:01:58 > 0:01:59THUNDER CRACKS AND BOOMS
0:01:59 > 0:02:02The quest to describe this mysterious power
0:02:02 > 0:02:08with a few simple units has been a challenge for the greatest of minds.
0:02:08 > 0:02:11But it has also had the most profound consequences
0:02:11 > 0:02:14for the way we live.
0:02:14 > 0:02:17This is the story of light, heat, and electricity.
0:02:29 > 0:02:32Hundreds of kilometres above our heads,
0:02:32 > 0:02:35a fleet of satellites watch over the Earth.
0:02:39 > 0:02:43What they can do seems almost magical, beyond belief.
0:02:45 > 0:02:47They can measure the thickness of sea ice
0:02:47 > 0:02:49with millimetre accuracy...
0:02:51 > 0:02:54..measure the temperature of our oceans
0:02:54 > 0:02:57or the subsidence of your house.
0:02:57 > 0:02:59And all of this only possible
0:02:59 > 0:03:03because of our precise ability to measure energy.
0:03:05 > 0:03:09Harnessing the power of light, heat and electricity
0:03:09 > 0:03:14has transformed our lives in ways no-one could have predicted.
0:03:17 > 0:03:21But how did we learn to measure energy with such precision?
0:03:26 > 0:03:29Until the late 17th century,
0:03:29 > 0:03:32no-one really understood anything about energy.
0:03:34 > 0:03:37Heat was considered a strange, invisible fluid.
0:03:39 > 0:03:43Electricity, a frightening and incomprehensible force of nature.
0:03:44 > 0:03:46And light?
0:03:46 > 0:03:49Something God-given that shone down from the heavens
0:03:49 > 0:03:51and ripened our crops.
0:03:51 > 0:03:53# Gloria, gloria!
0:03:55 > 0:03:57# Gloria, gloria! #
0:03:57 > 0:04:00It took the brilliance of Isaac Newton
0:04:00 > 0:04:03to revolutionise the understanding of energy,
0:04:03 > 0:04:06making the intangible tangible.
0:04:06 > 0:04:08And it started with light.
0:04:10 > 0:04:14The year was 1665 and, as the plague took hold of Britain,
0:04:14 > 0:04:17Newton fled his rooms at the University of Cambridge
0:04:17 > 0:04:19for the safety of his country retreat.
0:04:21 > 0:04:24He came here to Woolsthorpe Manor in Lincolnshire.
0:04:24 > 0:04:27And it's here that it's thought that he came up with a series
0:04:27 > 0:04:31of experiments that would change the way we think about light for ever.
0:04:40 > 0:04:42At the time of Newton's experiments,
0:04:42 > 0:04:45it was well known that if you pass light through a prism like this,
0:04:45 > 0:04:48then a spectrum of colour is produced.
0:04:50 > 0:04:51But what most people thought
0:04:51 > 0:04:55was that somehow the prism was colouring the light,
0:04:55 > 0:04:57but Newton thought differently.
0:05:03 > 0:05:05He wrote in a letter to the Royal Society,
0:05:05 > 0:05:11"Having darkened my chamber, I made a small hole in my window shuts
0:05:11 > 0:05:15"to let in a convenient quantity of the sun's light.
0:05:15 > 0:05:18"I place my prism at his entrance."
0:05:25 > 0:05:29Now, to prove that it isn't the prism that's colouring the light,
0:05:29 > 0:05:32Newton had a brilliant idea.
0:05:32 > 0:05:35What he did was to isolate one of the colours
0:05:35 > 0:05:37and he did that using a screen.
0:05:38 > 0:05:40I'm going to pick out the green.
0:05:41 > 0:05:44Now, if it was the prism that was colouring the light,
0:05:44 > 0:05:48if I put a second prism in front of this green,
0:05:48 > 0:05:50it should change the colour.
0:05:50 > 0:05:52But when Newton did that,
0:05:52 > 0:05:57what he saw was the same green colour on the wall.
0:05:57 > 0:06:00It wasn't the prism that was colouring the light.
0:06:04 > 0:06:06Newton had proved that it was the sunlight
0:06:06 > 0:06:09that was made up of all of these different colours.
0:06:09 > 0:06:13He'd unearthed the secrets behind the visible light spectrum.
0:06:16 > 0:06:18His account continued.
0:06:18 > 0:06:21"Light is a confused aggregate of rays,
0:06:21 > 0:06:24"imbued with all sorts of colours.
0:06:24 > 0:06:27"The blue flame of brimstone,
0:06:27 > 0:06:30"the yellow flame of a candle,
0:06:30 > 0:06:34"and the various colours of the fixed stars."
0:06:35 > 0:06:39Light was now something that could be analysed.
0:06:39 > 0:06:43Solving its mysteries would allow light to be manipulated
0:06:43 > 0:06:45and, most importantly of all, measured.
0:06:51 > 0:06:53Hypersensitive and extremely secretive,
0:06:53 > 0:06:56for years Newton didn't mention the experiment to anyone.
0:06:56 > 0:07:00But, finally, in 1672, he submitted his first formal paper
0:07:00 > 0:07:04about the experiment to the Royal society.
0:07:04 > 0:07:05When it was read to the fellows,
0:07:05 > 0:07:10it was met both with singular attention, and uncommon applause.
0:07:14 > 0:07:19This experiment sowed the seeds for the Age of Enlightenment.
0:07:19 > 0:07:21The age of science.
0:07:23 > 0:07:26When Newton discovered the visible light spectrum,
0:07:26 > 0:07:28what he didn't realise
0:07:28 > 0:07:31was that there was also light that he couldn't see.
0:07:32 > 0:07:34And we call it infrared.
0:07:37 > 0:07:40Over 100 years after Newton's discovery,
0:07:40 > 0:07:45astronomer William Herschel stumbled upon these invisible rays.
0:07:45 > 0:07:48Experimenting with the visible light spectrum,
0:07:48 > 0:07:50Herschel began taking the temperature
0:07:50 > 0:07:53of all the different colours.
0:07:53 > 0:07:57To his astonishment, when he placed the thermometer beyond the red,
0:07:57 > 0:08:00the mercury began to rise.
0:08:04 > 0:08:07I've got a much more sensitive thermometer here,
0:08:07 > 0:08:09called a thermocouple.
0:08:09 > 0:08:12You can see on the screen, which is measuring the temperature,
0:08:12 > 0:08:15there's a sudden surge out beyond the red.
0:08:15 > 0:08:17There we go. There's the spike. Wow!
0:08:19 > 0:08:23Herschel called these invisible rays "calorific rays,"
0:08:23 > 0:08:26but we know them today as infrared.
0:08:26 > 0:08:28And in fact, all the waves -
0:08:28 > 0:08:33infrared, radio waves, X-rays, microwaves, gamma rays -
0:08:33 > 0:08:35they're all like visible lights,
0:08:35 > 0:08:37certain forms of electromagnetic radiation.
0:08:37 > 0:08:40And all of this electromagnetic radiation
0:08:40 > 0:08:43are made up of photons of light of different wavelengths,
0:08:43 > 0:08:46some of which we can see, and some of which we can't.
0:08:46 > 0:08:49And it's the measurement of these invisible ways
0:08:49 > 0:08:52which is at the heart of 21st-century measurement.
0:08:58 > 0:09:03If light is made up of wavelengths of photons, what is heat?
0:09:04 > 0:09:07For millennia, this question remained a mystery.
0:09:09 > 0:09:14But its nature can best be seen using a heat-sensitive camera.
0:09:14 > 0:09:17If I take this piece of wood and hit it with a hammer...
0:09:20 > 0:09:23..then the infrared camera is picking up a change in temperature.
0:09:23 > 0:09:25It's getting hotter.
0:09:26 > 0:09:28So the mechanical energy of the hammer
0:09:28 > 0:09:30is causing an increase in heat.
0:09:34 > 0:09:37To understand what is happening in the wood,
0:09:37 > 0:09:41I've come to meet heat expert Michael de Podesta.
0:09:43 > 0:09:46Heat is the motion of molecules.
0:09:46 > 0:09:49Everything around you right now -
0:09:49 > 0:09:54inside it, the atoms and molecules are moving very, very fast.
0:09:54 > 0:09:59Each of those fat globules is being bombarded by the atoms around it.
0:09:59 > 0:10:01OK. So I can't see the atoms,
0:10:01 > 0:10:04but what I'm seeing is the effect that those atoms,
0:10:04 > 0:10:07and the heat, which is the movement of those atoms,
0:10:07 > 0:10:09has on the globules of fat.
0:10:09 > 0:10:11Exactly so.
0:10:11 > 0:10:12Heat is a type of energy.
0:10:12 > 0:10:17It's the energy that's tied up in the motion of the particles
0:10:17 > 0:10:20but temperature is a measure of their speed.
0:10:20 > 0:10:22Right. So actually when I touch something,
0:10:22 > 0:10:26and I'm detecting how hot it is, what I'm really detecting
0:10:26 > 0:10:29is how fast the molecules are moving on the surface.
0:10:29 > 0:10:32That is exactly what you are detecting.
0:10:32 > 0:10:33It's astonishing.
0:10:34 > 0:10:38To get to this molecular understanding of temperature,
0:10:38 > 0:10:42we first had to go through hundreds of years of experimentation
0:10:42 > 0:10:43and invention.
0:10:44 > 0:10:48And it all started in Renaissance Italy in the 16th century.
0:10:50 > 0:10:54MUSIC: "Symphony No. 94, 'Surprise' " by Joseph Haydn
0:11:04 > 0:11:07Using touch or seeing how the colour of something changes
0:11:07 > 0:11:08as you heat it up
0:11:08 > 0:11:11was about the only way we knew how to measure temperature
0:11:11 > 0:11:13for thousands of years.
0:11:13 > 0:11:15An accurate temperature measurement remained elusive
0:11:15 > 0:11:18until a breakthrough was made here in Italy
0:11:18 > 0:11:20towards the end of the 16th century.
0:11:20 > 0:11:25MUSIC CONTINUES
0:11:25 > 0:11:29And that moment came from the father of modern physics,
0:11:29 > 0:11:30Galileo Galilei.
0:11:32 > 0:11:35He revolutionised so many different areas -
0:11:35 > 0:11:40astronomy, physics, mechanics and my own subject of mathematics.
0:11:43 > 0:11:45But, for me, the really big surprise
0:11:45 > 0:11:48is that Galileo was one of the first
0:11:48 > 0:11:50to come up with a way of measuring temperature.
0:11:52 > 0:11:56At the time, he was reading a recently translated text
0:11:56 > 0:12:01by an ancient Greek mathematician and engineer, Hero of Alexandria.
0:12:01 > 0:12:03And it's thought that Hero's ideas
0:12:03 > 0:12:06inspired Galileo to look at temperature.
0:12:06 > 0:12:11Galileo invented what was then called the thermoscope.
0:12:11 > 0:12:15It was wildly inaccurate, but it was the world's first thermometer.
0:12:16 > 0:12:20A friend observed Galileo's ground-breaking experiment.
0:12:22 > 0:12:27"He took a small glass flask about as large as a small hen's egg
0:12:27 > 0:12:32"with a neck about two spans long and as fine as a wheat straw...
0:12:33 > 0:12:37"..and warmed the flask well in his hand.
0:12:38 > 0:12:42"When he took away the heat of his hands from the flask,
0:12:42 > 0:12:45"the water at once began to rise in the neck."
0:12:50 > 0:12:53What Galileo was exploiting here was the fact that,
0:12:53 > 0:12:56if you heat something up, like air, it expands.
0:12:56 > 0:12:59So the level of the water goes down.
0:13:00 > 0:13:01If I take my hands off,
0:13:01 > 0:13:03and let the flask cool down...
0:13:05 > 0:13:07..suddenly the level
0:13:07 > 0:13:08starts to up again.
0:13:08 > 0:13:12So suddenly we had the first way of measuring the temperature,
0:13:12 > 0:13:14instead using our hands or our eyes.
0:13:19 > 0:13:21Intrigued by the practical possibilities
0:13:21 > 0:13:26of temperature measurement, esteemed physician Santorio Santorio
0:13:26 > 0:13:28began making his own thermoscopes.
0:13:32 > 0:13:35He'd noticed that when his patients were feverish
0:13:35 > 0:13:38they felt hotter than usual and he wanted a way to prove it.
0:13:40 > 0:13:45He gave the thermoscope a scale, and, for the first time,
0:13:45 > 0:13:47recorded the temperature of a patient's mouth.
0:13:49 > 0:13:53But because it was open-ended, it was highly inaccurate,
0:13:53 > 0:13:56the results varying according to local air pressure.
0:13:58 > 0:13:59Over the next few years,
0:13:59 > 0:14:03Florence became a hotbed for thermometer experimentation.
0:14:05 > 0:14:09In 1657, the Medici family set up and funded
0:14:09 > 0:14:15the Accademia del Cimento, known as the Academy of Experimentation.
0:14:15 > 0:14:19Their motto was "proving and proving again"
0:14:19 > 0:14:22and temperature measurement was all the rage.
0:14:27 > 0:14:31It was a real fusion of art and science,
0:14:31 > 0:14:34using the skills of some of the finest glass blowers in the world.
0:14:37 > 0:14:40Thermometers became increasingly accurate.
0:14:40 > 0:14:46Water was replaced with alcohol and the stems became sealed.
0:14:46 > 0:14:52Designer Segredo built circular thermometers with 360 divisions.
0:14:52 > 0:14:55An idea he borrowed from the ancient Babylonians,
0:14:55 > 0:14:58who were the first to divide circles into degrees.
0:14:58 > 0:15:02It's why today we measure temperature in degrees.
0:15:08 > 0:15:11Having a thermometer became the height of fashion
0:15:11 > 0:15:13for any thinking man.
0:15:13 > 0:15:16The intangible had become tangible.
0:15:19 > 0:15:21By the end of the 18th century,
0:15:21 > 0:15:24we didn't really understand what temperature was.
0:15:24 > 0:15:27But we did have a means of measuring it.
0:15:27 > 0:15:30As for light, the opposite was true.
0:15:30 > 0:15:34We understood what it was but we couldn't measure it.
0:15:34 > 0:15:37However, the study of the other great form of energy,
0:15:37 > 0:15:40electricity, was in its infancy.
0:15:40 > 0:15:43THUNDERCLAPS
0:15:44 > 0:15:47For thousands of years,
0:15:47 > 0:15:49lightning and strange tales of torpedo rays
0:15:49 > 0:15:54were the only manifestations of this awesome force that we knew about.
0:15:57 > 0:16:00Striking fear into our hearts,
0:16:00 > 0:16:04all we could do was observe its blinding light and its searing heat.
0:16:05 > 0:16:10Before the 18th century, we had little idea what electricity was.
0:16:11 > 0:16:15We'd only puzzle over the effects of static electricity,
0:16:15 > 0:16:18marvel at the destructive power of lightning.
0:16:21 > 0:16:25So, how did we come to exploit and measure it so precisely?
0:16:29 > 0:16:33To answer that question, we have to go back 300 years
0:16:33 > 0:16:35to a world that was dark, cold and quiet.
0:16:35 > 0:16:38When the working day was determined by when the sun set,
0:16:38 > 0:16:40letters were delivered by horseback
0:16:40 > 0:16:43and electricity was just a spectacle, performed by showmen,
0:16:43 > 0:16:45who called themselves electricians.
0:16:47 > 0:16:50But this was also a time when people were becoming
0:16:50 > 0:16:53increasingly inquisitive about their world.
0:16:54 > 0:16:57The 18th century was a remarkable period
0:16:57 > 0:16:59in the history of measurement.
0:16:59 > 0:17:00It was the Age of the Enlightenment,
0:17:00 > 0:17:04when scientists were looking at the world around them with a keen eye,
0:17:04 > 0:17:05trying to find rational explanations
0:17:05 > 0:17:09for the phenomenon that they observed.
0:17:09 > 0:17:13And the strange force of electricity was coming under scrutiny.
0:17:18 > 0:17:21The breakthrough was made here in Pavia in Northern Italy.
0:17:21 > 0:17:24It was made by a charismatic and brilliant young scientist
0:17:24 > 0:17:26called Alessandro Volta.
0:17:26 > 0:17:28He became obsessed with the seemingly magical power
0:17:28 > 0:17:30of electricity.
0:17:30 > 0:17:34In a state of deep emotional distress, after a torrid love affair
0:17:34 > 0:17:36with a beautiful opera singer called Mariana,
0:17:36 > 0:17:39the love-sick Volta threw himself
0:17:39 > 0:17:42into the investigation of animal electricity.
0:17:44 > 0:17:48And the animal he studied was the torpedo ray -
0:17:48 > 0:17:51a fish capable of electrocuting its prey.
0:17:56 > 0:17:58What Volta was intrigued by was,
0:17:58 > 0:18:02what was inside the torpedo ray that was causing this electrical shock?
0:18:02 > 0:18:04When he looked inside its anatomy,
0:18:04 > 0:18:06what he found was a column of cells
0:18:06 > 0:18:09that seemed to be responsible for the shock.
0:18:09 > 0:18:11This is what he tried to copy.
0:18:12 > 0:18:15Volta must have played around with many different ideas,
0:18:15 > 0:18:20trying things, nothing worked, until suddenly he had a breakthrough.
0:18:20 > 0:18:24His lead came from the work of Luigi Galvani.
0:18:24 > 0:18:27Attaching copper and iron wires to a dead frog,
0:18:27 > 0:18:31Galvani discovered that he could make its legs twitch.
0:18:31 > 0:18:35He believed he'd found a strange new force inside the frog.
0:18:35 > 0:18:38Volta's brilliance was realising the phenomena
0:18:38 > 0:18:42was actually down to Galvani's use of two different metals.
0:18:44 > 0:18:48Inspired, he set about recreating the torpedo ray's cell column
0:18:48 > 0:18:51using alternating types of metal.
0:18:54 > 0:18:57First of all, he took a copper metal plate,
0:18:57 > 0:19:00put that one down on the bottom of the pile.
0:19:00 > 0:19:04And then, on top of that, he put a metal plate made out of zinc.
0:19:05 > 0:19:08And then the next ingredient was a piece of card
0:19:08 > 0:19:10soaked in a weak acid solution.
0:19:11 > 0:19:14And then that gets put on top of the zinc.
0:19:15 > 0:19:17So that's our first cell,
0:19:17 > 0:19:19and then he's going to make copies of these cells,
0:19:19 > 0:19:24build up this kind of pile, a little bit like in the torpedo ray.
0:19:24 > 0:19:27Another piece of acid, so that goes on there.
0:19:29 > 0:19:30To test this idea,
0:19:30 > 0:19:34what he did was to attach a wire to the bottom copper plate,
0:19:34 > 0:19:38another wire to the top zinc plate,
0:19:38 > 0:19:41and then what he hoped was he'd get an electrical shock
0:19:41 > 0:19:43when he joined these two together.
0:19:43 > 0:19:46To really test it, he placed the two ends of the wire
0:19:46 > 0:19:48on his tongue to actually feel the shock.
0:19:48 > 0:19:52Hopefully, I haven't made this too powerful. Let's try it out.
0:19:54 > 0:19:55It's quite gentle,
0:19:55 > 0:19:59but there is definitely the taste of the fizz of electricity.
0:19:59 > 0:20:02And the more cells I put on top of this, the bigger the current.
0:20:02 > 0:20:07To prove that I'm not just acting, I've got a little light bulb here.
0:20:07 > 0:20:11If I attach this to one end of the wire,
0:20:11 > 0:20:13and then to the other, there we go.
0:20:14 > 0:20:17The light lights up.
0:20:17 > 0:20:20But what's amazing about this is it's not just a spark
0:20:20 > 0:20:24of static electricity, or the shock of the ray.
0:20:24 > 0:20:29This is a gentle, continuous stream of electricity.
0:20:29 > 0:20:33This is the first time this had ever been done.
0:20:35 > 0:20:38And this is what really gave birth to the modern battery.
0:20:45 > 0:20:49In Volta's typical self-confident and flamboyant way
0:20:49 > 0:20:54he toured the lecture halls, showing off his great invention.
0:20:54 > 0:20:57Other scientists latched on to the discovery,
0:20:57 > 0:21:00using the cells in their own experiments.
0:21:03 > 0:21:05It would take hundreds of years
0:21:05 > 0:21:07before we fully understood electricity,
0:21:07 > 0:21:10but Volta had begun to unlock its secrets.
0:21:13 > 0:21:18Electricity, light and heat were no longer supernatural forces
0:21:18 > 0:21:20but tangible forms of energy
0:21:20 > 0:21:25that were attracting the greatest minds in science to their study.
0:21:25 > 0:21:29And these scientists soon realised better measurement
0:21:29 > 0:21:32would hold the key to harnessing their immense power.
0:21:36 > 0:21:39By the time Volta was creating the world's first
0:21:39 > 0:21:41continuous electrical current,
0:21:41 > 0:21:46thermometers had already been around for 200 years.
0:21:46 > 0:21:49But readings varied depending on whose model you used.
0:21:51 > 0:21:54It took Polish-born scientist Daniel Fahrenheit
0:21:54 > 0:21:56to make the first big leap
0:21:56 > 0:22:00in standardising temperature measurement.
0:22:00 > 0:22:05He chose mercury as it expands more uniformly than other liquids
0:22:05 > 0:22:09and is liquid over a wide temperature range.
0:22:09 > 0:22:13But his real innovation was to introduce two reliable
0:22:13 > 0:22:16and reproducible fixed temperature points,
0:22:16 > 0:22:19so a scale could be calibrated.
0:22:19 > 0:22:23At the low end, he chose the melting point of pure ice,
0:22:23 > 0:22:25at 32 degrees.
0:22:25 > 0:22:28And the upper end, 96,
0:22:28 > 0:22:31the temperature of human blood.
0:22:31 > 0:22:34This later changed to the more practical boiling point of water,
0:22:34 > 0:22:37at 212.
0:22:37 > 0:22:40Anders Celsius simplified things,
0:22:40 > 0:22:43choosing a 100-degree scale,
0:22:43 > 0:22:47based on the boiling and freezing points of water.
0:22:47 > 0:22:49His brilliance was to calibrate his thermometers
0:22:49 > 0:22:51to standard atmospheric pressure,
0:22:51 > 0:22:54making them accurate whatever the weather.
0:22:59 > 0:23:02Both scales are still used today.
0:23:02 > 0:23:04But it took the Industrial Revolution
0:23:04 > 0:23:06to show up their limitations.
0:23:08 > 0:23:12As the demands for ever greater accuracy and range grew,
0:23:12 > 0:23:14the Celsius and Fahrenheit thermometers
0:23:14 > 0:23:16were simply not up to the job
0:23:16 > 0:23:19in a fast-evolving world of heavy industry.
0:23:28 > 0:23:33By the of the 19th century, steam engines like this Watt engine
0:23:33 > 0:23:36were really driving the Industrial Revolution.
0:23:38 > 0:23:41They were pumping down mines, in distilleries,
0:23:41 > 0:23:46controlling the machines in factories across the country.
0:23:46 > 0:23:49This extraordinary engine at Papplewick will be pumping
0:23:49 > 0:23:52over a million and a half gallons of water a day
0:23:52 > 0:23:53for the citizens of Nottingham.
0:24:01 > 0:24:06The six huge furnaces would use 100 tonnes of coal a week,
0:24:06 > 0:24:08shovelled by a team of 14 men,
0:24:08 > 0:24:11working back-breaking shifts around the clock.
0:24:13 > 0:24:15The temperature inside this furnace
0:24:15 > 0:24:18is getting to over 1,000 degrees centigrade.
0:24:18 > 0:24:20That's heating water at the back
0:24:20 > 0:24:23which turns into steam, which, using some valves,
0:24:23 > 0:24:25drives the pumps of the Watt engine.
0:24:30 > 0:24:33Now, the thing is, when water turns into steam,
0:24:33 > 0:24:36the volume changes by a factor of 1,600,
0:24:36 > 0:24:38and that's where all the power comes from.
0:24:38 > 0:24:42Now, the pressure depends on the temperature inside this furnace.
0:24:42 > 0:24:45Get that temperature wrong, and the whole place blows sky-high.
0:24:48 > 0:24:51By the second half of the 19th century,
0:24:51 > 0:24:53boilers were exploding at a rate
0:24:53 > 0:24:56of almost one every four days in America alone.
0:24:58 > 0:25:01One of the worst incidents was later called
0:25:01 > 0:25:04the "Titanic of the Mississippi."
0:25:04 > 0:25:07LOUD EXPLOSION
0:25:07 > 0:25:09The American Civil War had just finished
0:25:09 > 0:25:11and the steam ship Sultana,
0:25:11 > 0:25:15packed with newly-released Union prisoners of war was returning home.
0:25:17 > 0:25:22At 2am on April 27th, 1865,
0:25:22 > 0:25:26her boilers exploded, tearing the ship apart.
0:25:29 > 0:25:33Over 1,700 lost their lives,
0:25:33 > 0:25:37in what remains one of America's worst maritime disasters.
0:25:40 > 0:25:45Steam power was changing our world but at a high cost.
0:25:45 > 0:25:49Thermometers simply wouldn't work at these high temperatures.
0:25:49 > 0:25:51The glass would break.
0:25:51 > 0:25:54And the Fahrenheit and Celsius scales themselves
0:25:54 > 0:25:57were far too inaccurate at recording temperatures
0:25:57 > 0:26:00so much higher than the boiling and freezing points
0:26:00 > 0:26:02that they were based on.
0:26:02 > 0:26:07A new means of measuring high temperatures was urgently needed.
0:26:07 > 0:26:12And the answer ultimately came from an unlikely source.
0:26:12 > 0:26:13Electricity.
0:26:15 > 0:26:19The breakthrough came in 1820, when a German scientist,
0:26:19 > 0:26:23Thomas Johann Seebeck, realised that if he took two wires
0:26:23 > 0:26:26of different metals and wound them round each other
0:26:26 > 0:26:28and put the two wires inside the furnace...
0:26:31 > 0:26:34..then took a compass and put it over the wires...
0:26:35 > 0:26:38..he discovered the needle of the compass moved.
0:26:38 > 0:26:43There was a magnetic field being cause by this wire.
0:26:43 > 0:26:46The difference in temperature between the end inside the furnace,
0:26:46 > 0:26:51and this end here is causing a difference in voltage potential,
0:26:51 > 0:26:54which is creating an electrical current running through this.
0:26:54 > 0:26:57The electrical current causes the magnetic field,
0:26:57 > 0:26:59and that's what's being picked up,
0:26:59 > 0:27:02when I put the compass over top of this.
0:27:02 > 0:27:06This simple observation is what led to the creation of a device
0:27:06 > 0:27:07called a thermocouple.
0:27:09 > 0:27:12In fact, a modern day thermocouple
0:27:12 > 0:27:15can actually measure this voltage difference.
0:27:15 > 0:27:18I can record that the heart of the furnace is going up...
0:27:18 > 0:27:19900 degrees...
0:27:19 > 0:27:23Look! It's just topped over 1,000 there.
0:27:23 > 0:27:25And, for me, the amazing thing
0:27:25 > 0:27:28is that we're using the measurement of electricity
0:27:28 > 0:27:32to actually find out what the temperature is inside this furnace.
0:27:32 > 0:27:35But before we could fully harness heat's power,
0:27:35 > 0:27:39we needed to understand what heat really was.
0:27:42 > 0:27:46In the 18th century, a popular theory among scientists
0:27:46 > 0:27:48was that heat was an invisible liquid
0:27:48 > 0:27:50that flowed in hot substances.
0:27:55 > 0:28:00It took keen amateur scientist, James Prescott Joule, in 1840,
0:28:00 > 0:28:02to start to unlock its mysteries.
0:28:04 > 0:28:08And it begins in rather an unlikely place.
0:28:08 > 0:28:09A brewery.
0:28:12 > 0:28:14Rather fond of beer,
0:28:14 > 0:28:17Joule realised that accurate temperature measurement
0:28:17 > 0:28:22was crucial to making a good pint in the family brewery.
0:28:22 > 0:28:24He became so good at measuring temperature,
0:28:24 > 0:28:27that he claimed you could measure it to an accuracy
0:28:27 > 0:28:30of one two hundredth of a degree Fahrenheit.
0:28:30 > 0:28:32But he also worked out something else,
0:28:32 > 0:28:36something that was crucial for scientists to understand.
0:28:36 > 0:28:41He devised a simple experiment that had an extraordinary result.
0:28:43 > 0:28:46Placing a paddle in a tank of water
0:28:46 > 0:28:49and turning it using the energy of a falling weight,
0:28:49 > 0:28:53he found that the temperature of the water went up.
0:28:53 > 0:28:57He also found that if the weight fell from even higher,
0:28:57 > 0:29:00the water got even warmer.
0:29:00 > 0:29:03Joule had discovered mechanical energy
0:29:03 > 0:29:05could be transferred into heat.
0:29:09 > 0:29:11It was a huge breakthrough.
0:29:11 > 0:29:15Heat wasn't an invisible fluid but a form of energy.
0:29:16 > 0:29:18But, at the time,
0:29:18 > 0:29:22the scientific community largely shunned his findings,
0:29:22 > 0:29:25refusing to believe this middle-class brewer
0:29:25 > 0:29:28could have anything meaningful to contribute to science.
0:29:28 > 0:29:33It took a chance meeting for Joule to be taken seriously.
0:29:33 > 0:29:35On honeymoon in the French Alps,
0:29:35 > 0:29:38and still obsessed with proving his theories of heat,
0:29:38 > 0:29:43Joule spent his time, not with his wife, but at waterfalls,
0:29:43 > 0:29:45measuring the difference in water temperature
0:29:45 > 0:29:47between the top and the bottom.
0:29:49 > 0:29:51It was here that he bumped into
0:29:51 > 0:29:54the world-renowned scientist Lord Kelvin.
0:29:57 > 0:30:01Their friendship would revolutionise our understanding of heat.
0:30:03 > 0:30:06Inspired by the work of Joule,
0:30:06 > 0:30:10Lord Kelvin set about devising a new temperature scale.
0:30:12 > 0:30:15No longer would temperature measurement
0:30:15 > 0:30:17be based on the boiling and freezing points of water,
0:30:17 > 0:30:21but on the very nature of heat itself - energy.
0:30:23 > 0:30:26Performing hundreds of gas experiments,
0:30:26 > 0:30:31Kelvin's goal was to find the coldest temperature in the universe
0:30:31 > 0:30:34and to use this as the base for his new scale.
0:30:39 > 0:30:42This is liquid helium
0:30:42 > 0:30:44and all this movement is caused by the molecules
0:30:44 > 0:30:46firing around inside it.
0:30:46 > 0:30:51But as the temperature drops, something strange starts to happen.
0:30:51 > 0:30:56The molecules slow right down until they virtually stop moving.
0:30:56 > 0:31:02The helium is close to a theoretical temperature called absolute zero.
0:31:02 > 0:31:08Kelvin calculated this to be minus 273 degrees Celsius,
0:31:08 > 0:31:11a temperature where molecules no longer move.
0:31:11 > 0:31:15There is no energy and therefore no heat.
0:31:16 > 0:31:18The inside of this flask
0:31:18 > 0:31:21is now one of the coldest places in the universe.
0:31:24 > 0:31:28Using absolute zero as the lower point of the scale,
0:31:28 > 0:31:31Kelvin had tied its base to the nature of heat.
0:31:32 > 0:31:34Yet, to make the scale practical,
0:31:34 > 0:31:38what was needed was a fixed point higher up.
0:31:38 > 0:31:42Kelvin died before his theories were put in to practice...
0:31:43 > 0:31:46..but the scientists that followed in his footsteps
0:31:46 > 0:31:50chose a strange phenomena called the triple point,
0:31:50 > 0:31:53where a substance can exist simultaneously
0:31:53 > 0:31:56as a gas, liquid and a solid.
0:31:57 > 0:32:02The reason measurement scientists like this triple point so much,
0:32:02 > 0:32:06is that it happens at a very precise temperature.
0:32:06 > 0:32:10So, at this point, we see the nitrogen in liquid and gas form.
0:32:13 > 0:32:17And we're going to reduce the pressure.
0:32:17 > 0:32:19As the pressure drops, so does the temperature,
0:32:19 > 0:32:23and the nitrogen begins to solidify.
0:32:23 > 0:32:25And we should be able to get... There we go.
0:32:27 > 0:32:32We've now captured the nitrogen in both liquid, gaseous and solid form.
0:32:32 > 0:32:38You can see this solid kind of, like, nitrogen ice sitting on top
0:32:38 > 0:32:41and the gas is bubbling underneath, pushing the solid up,
0:32:41 > 0:32:42and the liquid's below that.
0:32:44 > 0:32:46The old Fahrenheit and Celsius scales
0:32:46 > 0:32:50were fixed to the boiling and freezing points of water,
0:32:50 > 0:32:52which can vary enormously.
0:32:52 > 0:32:55The beauty of triple points is that they never vary
0:32:55 > 0:32:57by more than a few millionths of a degree.
0:32:59 > 0:33:02Now, with this idea of a theoretical absolute zero,
0:33:02 > 0:33:04and these triple points
0:33:04 > 0:33:07corresponding to different substances like nitrogen and water,
0:33:07 > 0:33:11finally the world had a precise scale to measure temperature.
0:33:13 > 0:33:14Oh!
0:33:15 > 0:33:19Half a century after his death, the kelvin was adopted
0:33:19 > 0:33:23as the international unit of temperature measurement
0:33:23 > 0:33:26and tied to a fixed point more accurate
0:33:26 > 0:33:29than Celsius and Fahrenheit could ever have imagined -
0:33:29 > 0:33:31the triple point of water.
0:33:33 > 0:33:37With it, incredible feats of engineering were now possible.
0:33:37 > 0:33:41From forging metals to growing crystals,
0:33:41 > 0:33:45the world finally had a temperature scale it could trust.
0:33:54 > 0:33:59Like heat, the story of electricity also took a giant leap forward
0:33:59 > 0:34:02during the Industrial Revolution.
0:34:04 > 0:34:08It was French maths prodigy and physicist Andre-Marie Ampere
0:34:08 > 0:34:11who was to make the next real breakthrough.
0:34:13 > 0:34:17Intrigued with Orsted's discoveries, he decided to further investigate
0:34:17 > 0:34:20the relationship between electricity and magnetism.
0:34:26 > 0:34:28Using apparatus very similar to this,
0:34:28 > 0:34:31he discovered that if he passed an electrical current
0:34:31 > 0:34:33between two parallel wires,
0:34:33 > 0:34:36it created a magnetic attraction between them.
0:34:36 > 0:34:38Now, I've beefed up the experiment a little bit
0:34:38 > 0:34:43by using these coils of wire, but if I turn on the electrical current...
0:34:44 > 0:34:48..the coils are then attracted to each other.
0:34:48 > 0:34:51And the key thing for us is the greater the electrical current,
0:34:51 > 0:34:53so if I beef that up a bit...
0:34:55 > 0:34:58..the greater the magnetic force between them.
0:35:00 > 0:35:04Ampere had found a new way to measure electricity.
0:35:06 > 0:35:09By measuring the strength of the magnetic force,
0:35:09 > 0:35:13he was able to build a machine to measure current
0:35:13 > 0:35:15called a galvanometer,
0:35:15 > 0:35:19named in honour of electrical pioneer Luigi Galvani.
0:35:21 > 0:35:24And there was a practical use to all this.
0:35:24 > 0:35:29Ampere's work was about to pave the way for modern communication.
0:35:32 > 0:35:35The first telegraph systems were basically a wire
0:35:35 > 0:35:38with a galvanometer stuck at each end.
0:35:41 > 0:35:45They worked by sending pulses of current down a wire,
0:35:45 > 0:35:47which then deflected these needles.
0:35:50 > 0:35:55Messages could now be sent at a speed of about six words per minute.
0:35:58 > 0:36:00But it took a grizzly murder
0:36:00 > 0:36:04for this new-fangled invention to be taken seriously.
0:36:04 > 0:36:06TRAIN WHISTLES
0:36:07 > 0:36:13In 1845, John Tawell poisoned his lover, Sarah Hart,
0:36:13 > 0:36:15with a deadly drink of prussic acid.
0:36:18 > 0:36:21Fleeing the scene, he jumped on a train to London.
0:36:23 > 0:36:28The alarm was raised and a telegraph message sent to Paddington Station.
0:36:30 > 0:36:32TELEGRAPH BEEPS
0:36:32 > 0:36:35"A murder has just been committed at Salt Hill,
0:36:35 > 0:36:38"and the suspected murderer was seen to take a first-class ticket
0:36:38 > 0:36:42"to London by the train which left Slough at 7:42pm.
0:36:43 > 0:36:46"He is in the garb of a Quaker."
0:36:49 > 0:36:51The message took ten minutes to get to London.
0:36:51 > 0:36:54The train took 50.
0:36:59 > 0:37:04On his arrival, Tawell was met and tailed by a London bobby.
0:37:05 > 0:37:09News of his spectacular arrest made every paper in the country.
0:37:09 > 0:37:12The power of electrical communication
0:37:12 > 0:37:13was clear for all to see.
0:37:17 > 0:37:21Soon telegraph lines were being laid across the world.
0:37:21 > 0:37:24A revolution in global communications was underway.
0:37:25 > 0:37:29But with no international system of measuring electricity,
0:37:29 > 0:37:31there were serious problems.
0:37:31 > 0:37:36If too much current was pushed down the line, the wires caught fire.
0:37:36 > 0:37:38Too little and the message never got through.
0:37:41 > 0:37:45With lots of competing and different units of electrical measurement in use,
0:37:45 > 0:37:48standardisation was urgently needed.
0:37:50 > 0:37:55And, in 1881, on the site of the Grand Palais here in Paris,
0:37:55 > 0:37:57that dream would become a reality.
0:38:03 > 0:38:05It was at the First Congress of Electricians,
0:38:05 > 0:38:09attended by 250 people from 28 different countries,
0:38:09 > 0:38:14that the ampere, the volt, the ohm, and the farad were finally defined.
0:38:14 > 0:38:16Ultimately, it would be the ampere
0:38:16 > 0:38:20that would become the international unit for electricity.
0:38:21 > 0:38:23Finally, the world had a standard
0:38:23 > 0:38:25for accurately measuring electricity.
0:38:25 > 0:38:30As the brains of the electrical world met behind closed doors,
0:38:30 > 0:38:32the French public were being treated
0:38:32 > 0:38:36to the greatest exhibition of electricity ever seen.
0:38:36 > 0:38:38All along the capital's tree-lined avenues,
0:38:38 > 0:38:42and in the exhibition halls, the latest electrical lighting,
0:38:42 > 0:38:45trams, telephones, generating systems, signalling devices
0:38:45 > 0:38:49would have been gathered for the congress and the whole world to see.
0:38:49 > 0:38:51It must have been an extraordinary sight.
0:38:51 > 0:38:56In fact, onlookers described it as a great blaze of splendour.
0:38:56 > 0:38:58It really marked the spirit of the age -
0:38:58 > 0:39:01a spirit of innovation and invention.
0:39:01 > 0:39:04But it was a young American engineer and entrepreneur
0:39:04 > 0:39:06who stole the show that year.
0:39:08 > 0:39:11His name was Thomas Edison.
0:39:13 > 0:39:17In two enormous rooms, filled with crystal chandeliers
0:39:17 > 0:39:20and hundreds upon hundreds of lights,
0:39:20 > 0:39:22the crowds were dazzled and amazed.
0:39:24 > 0:39:27But the invention that caught everyone's attention
0:39:27 > 0:39:33was his giant electrical generator, capable of lighting 1,200 lamps.
0:39:35 > 0:39:40With it were plans for the first complete electrical supply system.
0:39:40 > 0:39:44A system that would bring together the power of heat,
0:39:44 > 0:39:47electricity and light for the very first time.
0:39:48 > 0:39:52At its heart would be a steam-driven power station
0:39:52 > 0:39:54that would supply enough electricity
0:39:54 > 0:39:58to light over 100 businesses and private houses.
0:39:59 > 0:40:02Edison was about to light up our world.
0:40:10 > 0:40:14Six months later, Edison's dream would become a reality.
0:40:17 > 0:40:20On the 4th of September 1882,
0:40:20 > 0:40:23Edison switched on his Pearl Street Power Station
0:40:23 > 0:40:26and electrical current started flowing to 59 customers
0:40:26 > 0:40:30in Lower Manhattan, powering 400 lamps.
0:40:31 > 0:40:35The newspapers reported how, in a twinkling,
0:40:35 > 0:40:38the area bounded by Spruce, Wall, Nassau and Pearl Streets
0:40:38 > 0:40:40was in a glow.
0:40:42 > 0:40:45It marked the dawn of the electrical age.
0:40:47 > 0:40:49The world would never be quite the same again.
0:40:49 > 0:40:51Electricity had arrived.
0:40:56 > 0:40:59And even Edison must have been surprised by its popularity.
0:41:12 > 0:41:14Within two years,
0:41:14 > 0:41:17demand for Pearl Street electricity had rocketed tenfold.
0:41:17 > 0:41:20Electricity soon became a household commodity,
0:41:20 > 0:41:23like buying a load of coal or a box of matches.
0:41:23 > 0:41:25At least, if you could afford it.
0:41:25 > 0:41:26The next great challenge
0:41:26 > 0:41:29was measuring how much people were using.
0:41:30 > 0:41:36But the galvanometer and the units defined in Paris couldn't do this.
0:41:36 > 0:41:39Edison could have charged his customers
0:41:39 > 0:41:41based on the number of lamps they had.
0:41:41 > 0:41:45But soon he realised this was not a profitable way to do business.
0:41:47 > 0:41:52What he needed was a way to measure current usage over time
0:41:52 > 0:41:56and his solution was to use the principles of electroplating.
0:41:59 > 0:42:04Edison's first electricity meter basically consisted of a glass jar
0:42:04 > 0:42:10with two copper plates suspended in a copper sulphate solution.
0:42:10 > 0:42:14Now, as I pass electricity through the cell,
0:42:14 > 0:42:18then what happens is the atoms transfer from the solution
0:42:18 > 0:42:21onto the plate, making the plate heavier.
0:42:24 > 0:42:28Now, the key point here is the total mass of copper
0:42:28 > 0:42:31deposited on the plate is directly proportional
0:42:31 > 0:42:34to the total current running through the system.
0:42:34 > 0:42:39So now, if I switch off the electricity and take the plate out,
0:42:39 > 0:42:42you can see here the copper that's been deposited.
0:42:42 > 0:42:45Now, the amazing thing for me is that instead of measuring
0:42:45 > 0:42:48this rather elusive property of electricity,
0:42:48 > 0:42:50we're actually just measuring a change in weight.
0:42:50 > 0:42:53Finally, Edison had a way to charge his customers
0:42:53 > 0:42:55for the amount of electricity they used.
0:42:55 > 0:42:58He'd send out one of his employees to visit the cells.
0:42:58 > 0:43:01They'd take out the plate, measure the change in weight,
0:43:01 > 0:43:04and the customers would be billed accordingly.
0:43:04 > 0:43:06Now, it wasn't a brilliant system,
0:43:06 > 0:43:07but at least it was A system
0:43:07 > 0:43:10for measuring the amount of electricity that had been used.
0:43:16 > 0:43:18While the measurement of heat and electricity
0:43:18 > 0:43:22was making great advances in the industrial era,
0:43:22 > 0:43:25the quest to measure light had been all but forgotten.
0:43:26 > 0:43:30It took the emergence of street lights to change all this.
0:43:32 > 0:43:35Before Edison lit up our world using electricity,
0:43:35 > 0:43:38the very first lamps were powered by gas.
0:43:41 > 0:43:44It was the beginning of the 19th century -
0:43:44 > 0:43:47theft was on the rise and murder was commonplace.
0:43:49 > 0:43:51There was a desperate need for safer streets.
0:43:53 > 0:43:57And that came with the installation of the first public gas lights
0:43:57 > 0:44:00here in Central London in 1807.
0:44:02 > 0:44:05Demand for this new-fangled gas lighting soared
0:44:05 > 0:44:08and soon unscrupulous companies were cashing in,
0:44:08 > 0:44:12selling low-quality gas at high-quality prices.
0:44:12 > 0:44:14The outrage that ensued
0:44:14 > 0:44:20forced the government to introduce a new measure for light intensity.
0:44:20 > 0:44:23It was called candlepower and it was based on the brightness
0:44:23 > 0:44:26of a special candle made out of beeswax
0:44:26 > 0:44:31and naturally occurring oil taken from the head of a sperm whale -
0:44:31 > 0:44:33the spermaceti candle.
0:44:37 > 0:44:42The new unit was to be the light produced by one spermaceti candle
0:44:42 > 0:44:44weighing one sixth of a pound
0:44:44 > 0:44:48and burning at a rate of 120 grains per hour.
0:44:50 > 0:44:54It was the word's first attempt to try and produce a standard measure
0:44:54 > 0:44:57of light intensity but it was still very arbitrary.
0:44:57 > 0:45:00Light inspectors would go out, hold up greasy bits of paper,
0:45:00 > 0:45:03and try and compare the brightness of light
0:45:03 > 0:45:05coming from gas lamps to those of a candle.
0:45:05 > 0:45:08And it had a fundamental problem that still haunts
0:45:08 > 0:45:11the measurement of light intensity to this day.
0:45:11 > 0:45:15It depends entirely on our own perception of light.
0:45:26 > 0:45:29Now, this is the light produced by 100 candles.
0:45:29 > 0:45:33In a moment, I'm going to extinguish 50 of them.
0:45:33 > 0:45:37The problem is that the pupil in my eye expands and contracts
0:45:37 > 0:45:40to control the amount of light entering them,
0:45:40 > 0:45:43which means that when I extinguish half of them,
0:45:43 > 0:45:45it isn't going to look half as bright.
0:45:58 > 0:46:02Now, although the camera is recording a lower light condition,
0:46:02 > 0:46:06to my human eye, although I've got half as many candles,
0:46:06 > 0:46:09this looks as bright as it did before.
0:46:14 > 0:46:18It took a remarkable series of experiments in the 1920s
0:46:18 > 0:46:21to solve the riddle of human light perception.
0:46:23 > 0:46:28In an international study, 200 people aged 18 to 60
0:46:28 > 0:46:30underwent a series of tests
0:46:30 > 0:46:33to find out what colour wavelengths we see best
0:46:33 > 0:46:36and how our eyes combine these different colours
0:46:36 > 0:46:38to perceive brightness.
0:46:38 > 0:46:42Their work would lead to the creation of the candela,
0:46:42 > 0:46:44the unit we use to measure light today.
0:46:50 > 0:46:53'Here at the National Physical Laboratory,
0:46:53 > 0:46:57'Dr Nigel Fox can show me how unreliable my eyes are
0:46:57 > 0:47:00'as a means of measurement.'
0:47:00 > 0:47:02Yes, that's good. So let's measure.
0:47:02 > 0:47:06So, it looks a bit like a '70s disco in here, but...
0:47:06 > 0:47:11Yes. Yes, we can't quite reproduce the experiments of the 1920s.
0:47:11 > 0:47:13The equipment has all disappeared.
0:47:13 > 0:47:15But what we've tried to do
0:47:15 > 0:47:18is simulate the effect of that experiment here.
0:47:18 > 0:47:21So, Marcus, which of those lights looks brightest to you?
0:47:25 > 0:47:27Well, I'd say that the green one is...
0:47:27 > 0:47:30seems to be a lot brighter than the red and the blue.
0:47:30 > 0:47:34The red and the blue. Maybe the blue next and then the red third.
0:47:34 > 0:47:36But, yeah, the green certainly seems the brightest.
0:47:36 > 0:47:38Well, would it surprise you
0:47:38 > 0:47:40if I said the green is less than all of the others?
0:47:40 > 0:47:44- Oh, really? Less intense?- That's right.- So you're not tricking me?
0:47:44 > 0:47:46- No, no. This is... - What's this recording?
0:47:46 > 0:47:50This instrument is measuring the actual radiometric power
0:47:50 > 0:47:53that is coming from those different light sources.
0:47:53 > 0:47:56And as the instruments prove, my eyes really are deceiving me.
0:47:58 > 0:47:59That's extraordinary.
0:47:59 > 0:48:03The red is actually much more powerful than the green,
0:48:03 > 0:48:07- yet my eye is seeing the green as more luminous.- Exactly.
0:48:12 > 0:48:14The 1920s tests revealed
0:48:14 > 0:48:17not only that our eyes were much more sensitive
0:48:17 > 0:48:19to yellowish-green light,
0:48:19 > 0:48:20but that our age and sex
0:48:20 > 0:48:24also effect how we perceive the brightness of light.
0:48:25 > 0:48:29Compiling their results, the scientists came up with
0:48:29 > 0:48:32an average human perception of brightness.
0:48:32 > 0:48:37It's roughly equivalent to how a woman in her late 20s sees light.
0:48:39 > 0:48:41To this day, the definition of the candela
0:48:41 > 0:48:44remains locked to these findings.
0:48:47 > 0:48:49I can understand the need for the candela.
0:48:49 > 0:48:51I mean, having a unit of measurement
0:48:51 > 0:48:55which measures how the human eyes sees light is clearly useful.
0:48:55 > 0:48:57I mean, take this traffic light that's coming up.
0:48:57 > 0:49:00I want to know that it's bright enough that I'm going to see it
0:49:00 > 0:49:03but not so bright that it's going to dazzle me.
0:49:03 > 0:49:06The same applies to the car headlamps, street lamps,
0:49:06 > 0:49:09lights in our home - the list is endless.
0:49:15 > 0:49:17Because it's based on human perception,
0:49:17 > 0:49:21there's something rather odd about the candela as a unit.
0:49:21 > 0:49:25I mean, it's kind of the black sheep of the measurement family.
0:49:25 > 0:49:28And the candela's days are numbered.
0:49:29 > 0:49:33Today scientists are trying to base all measurement
0:49:33 > 0:49:37on the fundamental, unchanging laws of the universe.
0:49:37 > 0:49:41We've done it for the metre - basing it on the speed of light.
0:49:41 > 0:49:45And the second - on the movement of electrons inside an atom.
0:49:48 > 0:49:53Now the goal is to do the same for heat, electricity and light.
0:50:02 > 0:50:06Today, just as during the Industrial Revolution...
0:50:07 > 0:50:10..our ability to measure these energy units
0:50:10 > 0:50:12is failing to keep up with the demands of industry.
0:50:17 > 0:50:21Here at Rolls Royce, measuring and harnessing heat
0:50:21 > 0:50:24at temperatures higher than 2,000 degrees kelvin
0:50:24 > 0:50:29will help deliver more fuel efficient and powerful jet engines.
0:50:29 > 0:50:32Accurately measuring very high temperatures
0:50:32 > 0:50:34is a huge technical challenge.
0:50:35 > 0:50:38This is the high pressure turbine blade.
0:50:38 > 0:50:40This is the first rotating component
0:50:40 > 0:50:44that the gas stream would encounter, coming down from the combustor.
0:50:44 > 0:50:47Whereabouts is that in here? Are we downstream of the...?
0:50:47 > 0:50:49Downstream of the burners, yes.
0:50:49 > 0:50:52So this is exposed to extreme temperatures.
0:50:52 > 0:50:54It is indeed, and temperatures above its melting point.
0:50:54 > 0:50:56ABOVE its melting point?!
0:50:56 > 0:50:59So this would actually... SHOULD be melting, then? But... OK.
0:50:59 > 0:51:02- How do you make sure it doesn't melt?- We have to heavily cool them.
0:51:02 > 0:51:05So you can see some of the features that do that.
0:51:05 > 0:51:09The holes on the surface, there are passageways inside of the blade,
0:51:09 > 0:51:12finished items would have a coating on them as well,
0:51:12 > 0:51:14a thermal barrier coating,
0:51:14 > 0:51:17a ceramic layer which also takes a lot of the heat away.
0:51:17 > 0:51:21Despite state-of-the-art thermocouples, computer modelling,
0:51:21 > 0:51:24and thermal paints on the turbine blades,
0:51:24 > 0:51:27the experts here can only achieve an accuracy
0:51:27 > 0:51:29of about four degrees kelvin.
0:51:31 > 0:51:34Better accuracy isn't just a technical problem.
0:51:34 > 0:51:37The Kelvin scale itself loses accuracy
0:51:37 > 0:51:39the higher temperatures get.
0:51:44 > 0:51:46Today, new technologies
0:51:46 > 0:51:49are pushing temperature measurement to the absolute limit.
0:51:49 > 0:51:52Such that a new standard is critically needed.
0:51:52 > 0:51:55Here at the NPL heat lab, they think they might be close to cracking it.
0:51:59 > 0:52:01Michael de Podesta has built
0:52:01 > 0:52:04the most accurate thermometer in the world,
0:52:04 > 0:52:06an acoustic gas thermometer.
0:52:09 > 0:52:15It's the culmination of a 150-year story that began with Kelvin himself.
0:52:15 > 0:52:18What we are doing is we're determining temperatures
0:52:18 > 0:52:22in terms of the speed with which molecules are moving.
0:52:22 > 0:52:24What we measure is the speed of sound
0:52:24 > 0:52:27through argon gas trapped in this container down here.
0:52:27 > 0:52:31It seems extraordinary to be using sound,
0:52:31 > 0:52:33in a way, to be measuring temperature.
0:52:33 > 0:52:37Well, if you think about a sound wave,
0:52:37 > 0:52:41momentarily, gas is compressed and that heats up the gas
0:52:41 > 0:52:46and the gas then springs back and you're turning that thermal energy,
0:52:46 > 0:52:49the motion of... the microscopic motion of the molecules,
0:52:49 > 0:52:51back into mechanical energy.
0:52:51 > 0:52:55So sound is directly linked to temperature.
0:52:55 > 0:52:58So what we measure is the speed of sound
0:52:58 > 0:53:00and what we can infer very, very directly
0:53:00 > 0:53:02is the speed of the molecule.
0:53:10 > 0:53:13If it's successful, the acoustic gas thermometer
0:53:13 > 0:53:16will be as revolutionary for the measurement of heat
0:53:16 > 0:53:18as the atomic clock was for time.
0:53:18 > 0:53:19Just as Kelvin dreamt,
0:53:19 > 0:53:22it will create an absolute system
0:53:22 > 0:53:24based on one the fundamental constants of the universe,
0:53:24 > 0:53:28the Boltzmann constant - a magical number
0:53:28 > 0:53:31which relates the movement of molecules to temperature.
0:53:31 > 0:53:36When that happens, temperature will join the metre and the second
0:53:36 > 0:53:40in being tied to a universal constant of nature.
0:53:41 > 0:53:45And with it will come incredible precision,
0:53:45 > 0:53:49with devices capable of measuring accurately
0:53:49 > 0:53:52at temperatures hotter than the surface of the sun.
0:53:55 > 0:53:58It will give us greater control of heat,
0:53:58 > 0:54:00making engines more efficient and economical.
0:54:05 > 0:54:08Incredibly, in a lab just down the corridor
0:54:08 > 0:54:12from the acoustic thermometer, another breakthrough is underway.
0:54:19 > 0:54:22Here, JT Janssen and his team
0:54:22 > 0:54:25are revolutionising the measurement of electricity.
0:54:28 > 0:54:32And their work can be traced back to Volta's battery experiment.
0:54:34 > 0:54:38We now know if you break something down into its building blocks,
0:54:38 > 0:54:42atoms, you'll find a positively-charged nucleus,
0:54:42 > 0:54:45orbited by negatively-charged electrons.
0:54:46 > 0:54:50Metals like the copper and zinc used by Volta
0:54:50 > 0:54:54have electrons that readily detach from their nuclei.
0:54:54 > 0:54:57It is these loose-moving electrons
0:54:57 > 0:55:00that enable electricity to flow, forming a current.
0:55:02 > 0:55:05Using some of the strongest magnets on the planet
0:55:05 > 0:55:09and temperatures close to absolute zero,
0:55:09 > 0:55:13JT's team are controlling the movement of single electrons
0:55:13 > 0:55:17and counting them as they pass through their experiment,
0:55:17 > 0:55:19one at a time.
0:55:19 > 0:55:24Well, we've been working on this experiment for about ten years now.
0:55:24 > 0:55:28It's all related to trying to redefine the ampere,
0:55:28 > 0:55:30the unit for electrical current,
0:55:30 > 0:55:32in terms of a fundamental constant of nature
0:55:32 > 0:55:35and, in this case, that is the charge in an individual electron.
0:55:35 > 0:55:37And now we are at the level
0:55:37 > 0:55:41where we can control a billion electrons a second
0:55:41 > 0:55:43and we're only missing a few of those.
0:55:43 > 0:55:49The experiment will redefine our measure of electrical current
0:55:49 > 0:55:52using these individual electrons.
0:55:52 > 0:55:57They are fundamental particles, the same throughout the universe.
0:55:57 > 0:56:00For scientists, this is the goal -
0:56:00 > 0:56:04tying measurement to the unchanging laws of physics.
0:56:07 > 0:56:11And their work won't just impact on the world of measurement.
0:56:11 > 0:56:14Controlling the flow of single electrons
0:56:14 > 0:56:17is key to developing quantum computers.
0:56:17 > 0:56:20This next generation of technology
0:56:20 > 0:56:23will produce computers capable of calculations
0:56:23 > 0:56:26that are vastly beyond what is currently possible.
0:56:27 > 0:56:30They could simulate the human brain,
0:56:30 > 0:56:33model climate change in real-time
0:56:33 > 0:56:35and data storage using electrons
0:56:35 > 0:56:38would mean virtually limitless capacity.
0:56:42 > 0:56:45As we delve deeper inside the fabric of our universe,
0:56:45 > 0:56:49into the quantum world of subatomic particles,
0:56:49 > 0:56:53measurement is undergoing a fundamental and exciting change.
0:56:56 > 0:56:59We are now using the very building blocks of matter
0:56:59 > 0:57:02to help us measure the world around us.
0:57:06 > 0:57:08Even the black sheep of the measurement family,
0:57:08 > 0:57:12the candela, could soon be redefined,
0:57:12 > 0:57:14tied to the flow of photons of light.
0:57:20 > 0:57:24What started with our senses and crude guesswork
0:57:24 > 0:57:28is now getting down to the smallest building blocks of the universe,
0:57:28 > 0:57:32as our human urge for ever-greater precision drives us forward.
0:57:32 > 0:57:34CHEERING AND APPLAUSE
0:57:36 > 0:57:40Measurement has changed the course of science and civilisation.
0:57:41 > 0:57:44Now, as the quantum age approaches,
0:57:44 > 0:57:47our world is set to change once more.
0:57:53 > 0:57:57This is all part of a story which started thousands of years ago,
0:57:57 > 0:58:02when our ancestors began to measure time, length and weight.
0:58:02 > 0:58:05They were trying to understand the environment around them,
0:58:05 > 0:58:08to measure it and, ultimately, to manipulate it.
0:58:10 > 0:58:13But isn't that really what's still driving us today?
0:58:13 > 0:58:15Because measurement is the key
0:58:15 > 0:58:18to understanding our place in the universe.
0:58:33 > 0:58:36Subtitles by Red Bee Media Ltd